This invention relates to a magnetic separator for separating magnetic particles from a fluid by magnetic force.
FIGS. 1 and 2 illustrate a conventional magnetic separator of the type to which the present invention pertains. FIG. 1 being a vertical cross-sectional view and FIG. 2 being a perspective view thereof. This magnetic separator comprises a non-magnetic container 1 having inflow pipes 2 and 4 formed in its upper portion and corresponding discharge pipes 3 and 5 formed in its bottom portion. Inflow pipe 2 and discharge pipe 3 are for a fluid containing magnetic particles which are to be removed therefrom, while inflow pipe 4 and discharge pipe 5 are for washing water. The inside of the container 1 is divided into a particle trapping portion 7 and a particle accumulating portion 8 by a vertically-extending partition 6 having a plurality of through holes formed therein. A plurality of magnetizable wires 9 are stretched horizontally across the length of the container 1 with their ends secured to opposite walls of the container 1. A mechanical vibrator 12 for vibrating the magnetizable wires 9 extends through an opening formed in the upper portion of the container 1. As shown in FIG. 2, the container 1 is disposed between a pair of magnetic poles 13 with magnetize the magnetizable wires 9. The faces of the poles 13 are angled towards one another so that the strength of the magnetic field produced thereby within the container 1 linearly increases from the trapping portion 7 towards the accumulating portion 8.
During the operation of this conventional apparatus, a fluid 10 containing magnetic particles is introduced into the container 1 via inflow pipe 2, while washing water 11 is introduced via inflow pipe 4. The wires 9 are magnetized by the magnetic field produced by the poles 13, a magnetic attractive force which is proportional to the strength of the magnetic field and to the magnitude of the magnetic field gradient acts on the magnetic particles, and the magnetic particles contained in the fluid 10 are trapped by the magnetizable wires 9 as the fluid 10 flows therethrough.
While the fluid 10 is passing through the container 1, the mechanical vibrator 12 is operated to vibrate the fluid 10, the magnetizable wires 9, and the magnetic particles. The vibration forces the trapped magnetic particles to momentarily separate from the magnetizable wires 9, but upon separating, the magnetic attractive force causes them to reattach to the magnetizable wires 9. Each time the magnetic particles separate from the wires 9, they are moved by the magnetic field slightly in the direction of the accumulating portion 8 before they again attach to the magnetizable wires 9. Thus, as the magnetic particles repeatedly separate from and attach to the magnetizable wires 9, they are gradually conveyed from the trapping portion 7 into the accumulating portion 8 via the through holes in the partition 6. In the accumulating portion 8, the magnetic particles are removed from the magnetizable wires 9 by the downwards flow of washing water 11 through the accumulating portion 8, and the washing water 11 and the magnetic particles are together discharged from the container 1 via discharge pipe 5. The fluid 10, from which the magnetic particles have been removed, is discharged via outflow pipe 3.
The use of a mechanical vibrator 12 in this conventional magnetic separator to vibrate the magnetizable wires 9 and the magnetic particles creates the problem that the strength of the vibrations produced thereby varies depending on the distance of the wires 9 from the vibrator 12 and the path by which the vibrations are transmitted to the wires 9. As a result, the strength of the vibrations greatly varies over the length of each wire 9 and among the wires 9. At some locations along the wires 9, the vibrations are so strong that the magnetic particles become completely detached from the wires 9 and cannot reattach thereto. On the other hand, at other locations, the vibrations are too weak to make the magnetic particles detach from the wires 9, and the magnetic particles remain attached to the wires 9 at those locations and are not conveyed along the length of the wires 9 to the accumulating portion 8. Therefore, this conventional apparatus is unable to reliably separate the magnetic particles from the fluid in which they are contained and collect them.
Another problem with this type of conventional magnetic separator is that the strength of the magnetic field within the container 1 is a maximum at the end of the accumulating compartment 8 farthest from the trapping portion 7 (the far right end in FIG. 1). Therefore, the magnetic particles are continually pushed by the magnetic field against the right wall of the container 1 and accumulate there. It is possible to force the magnetic particles accumulated along the wall of the container 1 to separate from the magnetizable wires 9 by increasing the flow speed of the washing water 11. However, an increased flow speed causes some of the magnetic particles which were accumulated in the accumulating portion 8 to be carried back into the trapping portion 7 through the holes in the partition 6, resulting in a decrease in the recovery of magnetic particles.